Does the 250 Number mean total Cornea Thickness? If one is told they have a 476 Cornea thickness post lasik is that plenty to work with or does the 250 number entail a certain part of the Cornea only?
Thanks

DryEye wrote:Does the 250 Number mean total Cornea Thickness? If one is told they have a 476 Cornea thickness post lasik is that plenty to work with or does the 250 number entail a certain part of the Cornea only?Thanks

I'm not for sure, but I think in the case of Lasik, the the amount of cornea you're told you have left to work with would be the amount under the flap. Before you have a flap cut, it would of course be total cornea thinkness.

It is necessary for at least 250 microns of a healthy cornea to remain untouched to maintain stability. This does not commonly mean 250 micron total cornea, but 250 microns under the flap and under the ablation that is untoched.

Subtraction technique. The total thickness is measured and calculations of intended flap thickness and expected tissue ablation are subtracted.

Many doctors do a thickness test of the underlying stromal bed after creating and moving back the flap but before applying laser energy. This provides the actual flap thickness and residual corneal thickness, from which the expected tissue ablation is subtracted.

You've got 473 total corneal thickness (including the flap). You have 313 microns under the flap. So for future work in order to maintain the 250 minimum you have 63 microns of tissue which can be removed. So if you need an enhancement which would require the removal of more then 63 microns you're only option would be PRK on your flap.

PRK would remove top portion only vs lasik doing it internally with 63 microns of tissue for safety? Can a surgeon get it down (lasik enhancement) to a certain amount of tissue to remove safely when doing an enhancement - say 30 or 40 microns in this case?
With PRK they would have more to work with for removal if need be over a period of one's lifetime?
Do you know what the average (cornea left) is for most people after lasik?
How do the two differ in terms of corneal stability over long run?
With PRK one can do more than 63 microns if need be?
Also, I read here that once one does PRK over a flap that is the way it has to be done for additional enhancements down the road.
Would I have had more cornea left if I had chosen Intralase instead of microkeratome (VISX CustomVue)?
I think I would prefer lasik if I decide on an enhancement unless I am told that it isn't a wise choice.